#include <bits/stdc++.h>
using namespace std;
int main() {
  int n = 0;
  int box = 0;
  while (true) {
    int k;
    cin >> k;
    if (-1 == k)
      break;
    else {
      if (k % 2 == 0) {
        box += k;
        n++;
      }
    }
  }
  if (0 == n)
    cout << "0.00";
  else
    cout << fixed << setprecision(2) << double(box) / n;

  return 0;
}